1. Field of the Invention
The present invention relates to a technique for printing images on a print medium by ink ejection.
2. Description of the Related Art
Ink-jet printers for forming ink dots into images on print media by ejecting ink droplets are widely used as devices for outputting images created by computers and digital cameras.
When line-drawing images such as characters and illustrations are printed by an ink-jet printer, the ink sometimes bleeds along the outlines of the line-drawing image. Such ink bleeding is attributed to the fact that the ink ejected into the line-drawing area accumulates without being absorbed by the print medium, and flows out toward the areas not intended to form dot therein.
In particular, ink dots tend to elongate in the direction of main scan when they are formed while the print head is moved in the direction of main scan, so contour lines extending parallel to the direction of main scan are prone to ink accumulation and bleeding. Also, this kind of bleeding occurs not just with the contour areas of line-drawings, but also in cases when a contour is formed with different colored high-density areas adjacent to each other.
Accordingly, an object of the present invention is to reduce ink bleeding in an outline portion parallel to the main scan direction in a printing device for printing images by ejecting ink droplets during main scans.
In order to attain the above and the other objects of the present invention, there is provided a method of recording by forming ink dots on a print medium during main scans. The method comprises the steps of: generating dot data from image data indicative of a image to be printed, the dot data representing a state of dot formation at each pixel; identifying a transverse contour line of a specific type image area represented by the dot data, the transverse contour line being parallel to a main scan direction, the specific type image area being composed of pixels at which specific tones are recorded by forming ink dots; adjusting the dot data so as to regularly reduce amounts of an ink for forming ink dots on the identified transverse contour line; and recording tones of pixels on the print medium by forming ink dots in response to the adjusted dot data, wherein this step includes the step of recording each of two pixels which are adjacent in the main scan direction, during each of different main scans, respectively.
In the printing method of the present invention, the dots forming an image on adjacent pixels in the main scan direction are each formed during different main scans. This makes it possible to lengthen the time intervals of ink drop ejection onto this kind of adjacent pixel on the transverse contour line on which bleeding occurs easily. This process reduces the size of the ink accumulations, to thereby suppress bleeding that occurs at transverse contour lines. As a result, it is possible to print sharp images of line-drawings including a text image.
The present invention can be realized in various forms such as a method and apparatus for printing, a method and apparatus for producing print data for a printing unit, and a computer program product implementing the above scheme.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.